The horizontal (top and bottom) Splitting bars of border layout bleed through Windows. In fact the splitting bar comes though any part of a window and the windows content (including flash content: e.g. Open Flash Charts).

The vertical splitter bars to do bleed through.

The cursor will change to the spilt move cursor and clicking will move the spilt bar rather than interacting with the content in the window or moving the window.

This makes it very difficult move the window or interact with it if the title bar of the window happens to be over a splitting bar.